Bug 136941

Summary: Xlib: Maximum number of clients reached
Product: [openSUSE] SUSE LINUX 10.0 Reporter: Olaf Dabrunz <odabrunz>
Component: X.OrgAssignee: Stefan Dirsch <sndirsch>
Status: RESOLVED WONTFIX QA Contact: Stefan Dirsch <sndirsch>
Severity: Normal    
Priority: P5 - None CC: eich
Version: Final   
Target Milestone: ---   
Hardware: All   
OS: SuSE Linux 10.0   
Whiteboard:
Found By: Development Services Priority:
Business Priority: Blocker: ---
Marketing QA Status: --- IT Deployment: ---

Description Olaf Dabrunz 2005-12-05 16:04:14 UTC 
od@blackberry:~> xterm
Xlib: connection to ":0.0" refused by server
Xlib: Maximum number of clients reached
xterm Xt error: Can't open display: :0.0

My system has many open connections from X clients, mainly because every w3m
starts a separate w3m-imgdisplay process to render pictures to the current
window.

blackberry:~ # netstat -n | grep X11 | wc -l
248

Having that many client connections is obviously a problem on the client side.
It should be possible to reduce the number of client connections when w3m has
better handling of sessions. 

As this is not available (yet?), I wonder if increasing the maximum number of
connections would be acceptable:

--- programs/Xserver/include/misc.h.orig        2005-12-05 17:01:05.000000000 +0100
+++ programs/Xserver/include/misc.h     2005-12-05 17:02:36.000000000 +0100
@@ -92,7 +92,7 @@ extern unsigned long serverGeneration;
 #ifndef MAXSCREENS
 #define MAXSCREENS     16
 #endif
-#define MAXCLIENTS     256
+#define MAXCLIENTS     512
 #define MAXDITS                1
 #define MAXEXTENSIONS  128
 #define MAXFORMATS     8
Comment 1 Olaf Dabrunz 2005-12-06 13:17:05 UTC 
This is really biting me.

Tentatively increasing severity to major.
Comment 2 Stefan Dirsch 2005-12-06 13:31:32 UTC 
# cvs annotate misc.h
[...]
3.14         (dawes    14-Aug-98): #define MAXCLIENTS   256
[...]

# cvs log misc.h
[...]
revision 3.14
date: 1998/08/14 13:35:50;  author: dawes;  state: Exp;  lines: +2 -2
fix some build problems
change the connection limit stuff
[...]

# cvs diff -u -r3.13 -r3.14 misc.h
[...]
@@ -94,7 +94,7 @@
 #ifndef MAXSCREENS
 #define MAXSCREENS     4
 #endif
-#define MAXCLIENTS     128
+#define MAXCLIENTS     256
 #define MAXDITS                1
 #define MAXEXTENSIONS  128
 #define MAXFORMATS     8
Comment 3 Stefan Dirsch 2005-12-06 15:54:24 UTC 
MAXCLIENT = 512 seems to be already prepared.

programs/Xserver/include/resource.h
[...]
/* bits and fields within a resource id */
#define RESOURCE_AND_CLIENT_COUNT   29                  /* 29 bits for XIDs */
#if MAXCLIENTS == 64
#define RESOURCE_CLIENT_BITS    6
#endif
#if MAXCLIENTS == 128
#define RESOURCE_CLIENT_BITS    7
#endif
#if MAXCLIENTS == 256
#define RESOURCE_CLIENT_BITS    8
#endif
#if MAXCLIENTS == 512
#define RESOURCE_CLIENT_BITS    9
#endif
Comment 4 Olaf Dabrunz 2005-12-06 16:31:34 UTC 
The additional memory space used in the X-Server does not seem to increase that
much. A few arrays of pointers are bigger, and this:

typedef struct _ClientResource {
    ResourcePtr *resources;
    int         elements;
    int         buckets;
    int         hashsize;       /* log(2)(buckets) */
    XID         fakeID;
    XID         endFakeID;
    XID         expectID;
} ClientResourceRec;

[...]

ClientResourceRec clientTable[MAXCLIENTS];


The only point seems to be that the number of available RESOURCE_IDs decreases
from about 2 million (2^21) to one million (2^20):

#if MAXCLIENTS == 512
#define RESOURCE_CLIENT_BITS    9
#endif
/* client field offset */
#define CLIENTOFFSET        (RESOURCE_AND_CLIENT_COUNT - RESOURCE_CLIENT_BITS)
/* resource field */
#define RESOURCE_ID_MASK        ((1 << CLIENTOFFSET) - 1)


Egbert, what do you think?
Comment 5 Egbert Eich 2005-12-07 11:37:52 UTC 
A while ago we were asked to increase this number because the broken IBM Java implementation expected to open up bzillions of clients. We strongly encouraged IBM to fix this - and they did.
Here w3m seems to be broken - and should be fixed. We would have to review the code in may places if more than 256 clients will actually work without problems lurking in some remote corners. 
Being that this is really a corner issue and not a popular request I will rather spend my time on other issues. In amy case this warrent a severity of "major'.
Also, where is the limit? Is 512 really enough?

Maybe you want to explore the issue yourself and roll an Xserver with MAX_CLIENTS set to 512. If you don't see problems we may want to explore the issue further after SLES10.
Comment 6 Olaf Dabrunz 2005-12-07 13:30:56 UTC 
I can see your points.

Thanks for commenting on this.

In the meantime I have had some ideas on how to solve the problem in w3m more
quickly, including
    - using one w3mimgdisplay server for all w3ms running on a client for a
      given user on a given display
    - use only one w3m and add a feature to switch between sessions/tabbars

Aternatively maybe I can build and test an Xserver with 512 clients myself.

I cannot spend much time on this either, but I will see what can be done...

Thanks again!